My guess is because this is not an Android phone and it is important to be able to chat with Android and iPhone users. The real question is why would iPhone and Android users install this app?

https://www.hmd.com/en_in/about-hybrid-phones

Edit: Requiring Google Play login to use this express chat app is pretty stupid in my opinion. Why do apps require Google Play login? Especially a Chinese app? I am on an Android phone with Google play. I am just not signed in to Google play. I installed this app with Aurora store. The app simply throws me back to Play Store which tells me to sign in. Why?

https://play.google.com/store/apps/details?id=com.moon.expre...